Television viewing screen



June 13, 1944. o. H. scHADE 2,351,294

TELEVISION VIEWING SCREEN Original Filed 001:. l7,' 1940 TelevisionMMAMAA Gear Movemenf INVENTOR 0H0 H. Schade.

Patented June 13, 1944 2,351,294 remvisron'vmwmc some:

Otto u. some, West Caldwell, N. to Radio Corporation of America,

of Delaware 1., assllnor a corporation Original application October 17,1940, Serial No. 361,503, now Patent No. 2,302,147, dated November 17,1942. March 24, 1942,

6 Claims.

My invention relates to the reception of television images in naturalcolor and particularly to reflection and luminescent-type screens forsuch reception, and is a division of my copending application, nowissued as Patent 2,302,147, November 17, 1942.

It has been proposed to transmit television images in color bysuccessively exposing a photosensitive target electrode throughsuccessively displaced primary color filters to the illuminated objectof which an image is to be transmitted. Use is made at the transmitterof a rotating filter containing two or more color filters, and a similarrotating filter at the receiving location is provided, such as in thepath of the light between a cathode ray tube or light valve and theobserver to recreate the television image in natural colors. The use ofsuch a rotating shutter at the receiving location is objectionable insome cases because of the space required, inasmuch as it must beapproximately twice the diameter of the cathode ray tube or light valvescreen. A further disadvantage resides in the fact that considerablelight is lost by such a filter system so that the light which may becreated or controlled by the cathode ray or projection tube is notefiectively utilized.

It is an object of my invention to provide a viewing screen for colorpicture presentation wherein all of the light of the various colorscomprising the picture is effectively utilized; and

it is a further object to provide a screen and system for recreatingcolored images which will occupy considerably less space than priorscreens and systems; It is a still further object to provide a screenand image recreating system wherein substantially all of the lightincident on the screen is converted to useful light representative ofthe recreated image. These and other objects, features and advantages ofmy invention will become apparent when taken in connection with thefollowing description and accompanying drawing wherein:

Figure 1 shows an image projection system and screen made in accordancewith my invention;

Figure 2 is a perspective view of the type of screen shown in Figure 1;and

Figure 3 is an end view of the screen shown in Figure 2 showing themethod of rotating the various elements of the screen.

In accordance with one teaching of my invention,,I provide areflection-type viewing screen comprising a suitable number of opaquesegmented sections preferably of twisted triangular prismatic form,successive faces of which are Divided and this application Serial No.435,928

made selectively reflective to light of various colors,such as red, blueand green, and I rotate these prismatic segments in a sequencedetermined by the recreation of the television image. Further inaccordance with my invention 1 provide a system wherein the recreatedimage consists of various intensities of ultra violet light, this lightbeing projected upon a screen having one or more segments which arepreferably of twisted triangular prismatic form, the surfaces beingresponsive to convert the ultra violet light into the primary colors,such as red, blue and green. In each of these preferred modifications ofmy invention the liberation of light of suc- .cessive colors iscontrolled by the viewing screen itself and is not dependent upon thecolored filters interposed between the light source and the viewingscreen.

A colored image to be televised is broken up at the transmitting stationinto a series of image fields of representative colors.v A single frameof the television image may comprise three successive fields of red,blue and green successively scanned to generate a succession of imageimpulses representative of the optical image to be transmitted. Thetelevision image may be received by a conventional television receiveri, shown schematically in Figure 1, having a cathode ray tube 2 capableof recreating the television image which appears due to persistance ofvision as a black and whit replica of the original image such as upon afluorescent screen 3 associated with the tube 2. The luminescentmaterial comprising the screen 3 may be of mixed sulphides, theprincipal requirement being that each of the primary colors is presentin the light generated by the screen. Preferably th luminescentmaterials used for the screen 3 should have a rapid phosphorescent decaytime, a property which is inherent in certain well known mixed sulphidescreens. In accordance with known systems the image replica, which'whenviewed directly appears black and white on the screen 3, may be viewedin its natural colors by rotating a filter disc containing successivelydisplaced filters transparent to the primary colors and viewing thescreen through this disc which is operated in synchronism with acorresponding filter disc or mechanism at the transmitter. However, inaccordance with my invention and as shown by Figure 1, th light formingthe black and white replica appearing on the fluorescent screen 3 isprojected and focused such as by a lens system I, which may be of thetransmission or reflection ultra Violet light.

.type, upon a viewing screen I on whichthe televised image appears inits natural colors.

Referring to Figure 2 which shows a perspective view of the screen I,the screen comprises one or more individual light developing orreflecting members ll having an equilateral triangular,

twisted by an angle of approximately 120 from one end of the members 30to the opposite end. The cross-section of each of the members 30 in aplane normal to the axis of the members is preferably triangular and thehelically twisted surfaces may be said to be generated by moving thelines bounding the cross-section along the axis while revolving thebounding lines about the axis. The surfaces will have a progressivelyuniform surface, provided the movement of the generating lines about theaxis is proportional to the displacement along the axis, although thisdisplacement may be made non-linear, provided the vertical deflection ofthe scanning spot of light is non-linear with time to a correspondingdegree.

The members 30 are supported with their axes parallel and coplanar toone another and free to rotate; such as in a clock-wise direction asshown.

I have shown in Figure 3 means for rotating the members 30 continuouslycomprising a gear wheel on each of members 30 with an intervening gearto provide rotation in .the same direction. As the members 30 rotate inaccordance with the frame'rate of scanning, a section of line width willmove progressively from the top of the memhere to the bottom, which isthe direction of vertical scanning. The members are shown in Figure 2 inan instantaneous position at which an elemental line may bedrawn alongone of the surfaces of the members, the said-line being continuous overthe entire width of the screen comprising the members 30. The screenmembers are so synchronized with the frame rate of scanning that thelight beam is incident on the members along this line as it progressesfrom the top to the bottom of the members during rotation thereof Thusas shown in Figure 2, the screen may be scanned along the line 3| whichisprogressively and during successive scannings displaced in thedirection of vertical scanning corresponding to the direction of theline 32. In accordance with my invention, each of the faces of theprismatic members 30 such as the faces 33, 34 and 35 are made toliberate light of one of the primary colors such as red, blue or green.Thus the faces may be made reflective to individual primary colors orthese faces may be provided with coatings of different luminescentmaterials which successively luminesce with the three primary colorsunder excitation such as Thus whether the faces are reflective tovisible light or subjected to ultra violet light, light corresponding tothe three primary colors is liberated. Since the members 30 arehelically twisted by an angle of 120 from one end thereof to the otherand are rotated in syn-' chronism with the frame rate of scanning. the

light beam impinges on the members at a time when a surface of elementalline width is in the proper position for reflecting light to theobserver. Bince the curvature from top to bottom of the members iscontinuous, a scanning beam of light having very small cross-section ispreferable.

As the scanningbeam approaches the lower ends of the members Ill and.following scansion, is returned to the top of the members, the angulardisplacement of the surface along the length of the members places asurface capable of libcrating a different color in position forscanning. Since the light beam return time or fly back" time is finite,somewhat less than the full-length of the members is scanned in thevertical direction. However, a helical displacement of somewhat lessthan 120 may be provided, depending upon the=time required for thereturn or fly back time, whereupon the full-length of the members may bescanned.

I have described the members 30 as being of triangular cross-section, sothat they may be aligned with a minimum of spacing between adiacentmembers.

However, a single multi-face member may be used as the viewing screenand, in this case, the member may have more than three surfaces. Thus amember having an equilateral polygonal cross-section with more thanthree faces but preferably an integral multiple of three faces may beused, each face liberating a different primary color such as in regularsequence of red, blue and green. Obviously, such a single screen membermay have surfaces liberating a number of colors greater than three, suchas for a four or flve color system of television transmission. Thedimensions of each face of a single member screen correspond to fullimage size and the member is rotated at constant speed.

As indicated above the members 30, instead of having threereflectivesurfaces, reflective to different colors of light,.may havethe three surfaces coated with luminescent materials, each of which hasa different spectral response characteristic when subjected to ultraviolet radiation. When utilizing a viewing screen of this type, thefluorescent screen of the television receiving tube or the light sourcefor a light valve is constructed to produce ultra violet light.- Thusthe fluorescent screen 3 may consist of pure zinc silicate having nofluorescent activator which, when scanned by an electron beam in amanner well known in the art, recreates an ultra violet television imagewherein the light and shade areas of the original optical image arerecreated in various intensities of ultra violet light. In accordancewith this teaching of my invention, the ultra violet light from asequentially scanned cathode ray tube or light valve is projected uponthe segmented sections of prismatic form, the faces of which areresponsive to the ultra violet light to generate various colors such asred, blue and green. One face of each of the triangular prismaticmembers 30 is provided with a coating ll of material which, whensubjected to ultra violet light, produces red light, whereas the coating42' on one adjacent face produces blue, and the coating 43 on the otheradjacent face produces green light under the influence of the ultraviolet light from the fluorescent screen 3. For example, a luminescentmaterial comprising 10 to 30% of zinc sulphide mixed with 70 to cadmiumsulphide may be used to form the luminescent material coating 4| capableof giving red light. Silver activated zinc sulphide may be used jacentsurfaces, means to support said prismforthe luminescent blue responsivecoating 42, and 30 to 40% zinc cadmium sulphide with 60 to 70% zincsulphide may be used for the green responsive coating 43.

In operation the television image is received and converted into a lightand shade replica wherein each of three successive fields of scan,- ningis representative of a different primary color of the original opticalimage. Depending on the transmission standards chosen, the image may betransmitted at twenty frames per second, each frame consisting'of threecolor fields successively red, blue and green or a vertical scanningfield frequency .of 60 cycles per second. The horizontal line definitionis independent of the field frequency and may be chosen in accordancewith the available frequency band width for transmission. With avertical field frequency of per second the members having three facesshould be rotated at a rate of 1200 revolutions per min ute, whereas for40 frames and 120 fields per second the rate should be 2400 revolutionsper minute.

In my above-mentioned original application I disclosed other types ofscreens whereby my' objects may be obtained and while in thisapplication I have indicated only several preferred embodiments of myinvention of which I am now aware and have also indicated only onespecific application for which my invention may be employed, it will beapparent that my invention is by no means limited to the exact formsillustrated or the use indicated, but that many variations may be madein the particular structure used and the purpose for which it isemployed without departing from the scope of my invention as set forthin the appended claims.

I claim:

1. A viewing screen scanned by a beam of light for television receptioncomprising an equilateral prism having similar warped lateral surfaceseach being ofa mater al which liberates li ht of a different color fromthe others when scanned by said beam.

2. A viewing screen scanned by a beam of light for television receptioncomprising a plurality of elongated prisms arranged side by side withtheir axes lying parallel to one another, each of said prisms havingthree similar warped lateral surfaces, each of the surfaces of each ofsaid prisms being of a material which liberates light of a differentprimary color from the others when scanned by said beam.

3. In combination with means for developing a beam of light displaced intwo mutually perpendicular directions at difi'erent rates over an imagearea, a viewing screen to intercept said beam of light and form anoptical image observable by persistence of vision said screen comprisinga prism with a. plurality of similar warped surfaces surrounding anaxis, each of said surfaces being of material capable of liberatingdiffused light of a different primary color from adwith its axisparallel to the direction of the lower rate of displacement of said beamof light so that during rotation thereof only an elongated elementalarea extending in the direction of the higher rate of scanning isexposed in a normal image receiving position to said first-mentionedmeans at any instant of time, said area progressing axially withrotation of said member and a means to rotate said member about its axisthrough the angle subtended by one of said surfaces during thedisplacement of said beam of light over said image area at said lowerrate.

4. Apparatus as claimed in claim 3 wherein said first-mentioned meansdevelops a beam of ultra-violet light and each of said surfaces iscoated with luminescent material. the composition of the said materialon one surface differing from that on adjacent surfaces whereby light ofa different color is developed on each adjacent surface when subjectedto said. beam of ultraviolet light.

5. In combination with means for developing a beam of light scanned overan image area in two mutually perpendicular directions at differentrates, a viewing screen to intercept said beam of light and form anoptical image observable by persistence of vision, said screencomprising a plurality of rotatable prisms each having three similarwarped surfaces surrounding an axis, each of the surfaces of each prismbeing of a material capable of liberating diffused light of a differentprimary color from that of adjacent surfaces, means to support saidprisms with their axes in substantially a single plane parallel to thedirection of the lower rate of scanning by said beam and means to rotatesaid members at a uniform rate about their respectiveaxes through anangle of one hundred twenty degrees during the displacement of said beamof light over said image area at the lower rate of scanning.

6. In combination with means for developing an ultra-violet light beamscanned over an image area in successive series of mutually displacedparallel paths, a viewing screen including a plurality of rotatableprisms each having three similar warped surfaces surrounding an axis,each surface of each of said prisms being coated with luminescentmaterials of a composition differing from that of the coating onadjacent surfaces said luminescent materials being chosen to. liberatevisible light of 'a different color from each surface of each prism whenscanned by said ultra-violet light beam, means to support said prismswith their axes parallel to one of said directions of scanning and meansto rotate said members at a uniform rate about their respectivelongitudinal axes through an angle of one hundred twenty degrees duringthe displacement ofsaid beam of light over said image area in said oneof said directions. O'I'IO H. SCHADE.

